Castumi: A demon of invisibility, Castumi appears as part of an invisibility spell outlined in the Clavicula Salomonis. According to this text, Castumi serves Almiras, the demonic Master of Invisibility.
Castumi can also be found associated with invisibility spells in Mathers' translation of the Sacred Magic of Abramelin the Mage.
SOURCE:
The Dictionary of Demons written by Michelle Belanger